The present invention relates generally to the detection of cancer and precancerous conditions and more particularly to a method of detecting the presence of cancer and/or precancerous conditions in tissues and/or cells using native fluorescence excitation spectroscopy. The present invention also relates to the detection of the presence of cancer-related proteins in tissues and/or cells using native fluorescence excitation spectroscopy.
Because a sufficiently effective method has not yet been developed to prevent cancer, cancer research has focused on the most effective ways to treat cancer. As different as the various forms of treatment have been--ranging from excision to radiation to chemotherapy--all treatments have relied upon one crucial step, the detection of cancer. The importance of detection cannot be stressed enough. Early detection not only indicates the presence of cancer (or of a precancerous condition) but also may give an indication as to where the cancer originated and what type of treatment will be the most safe and effective. In addition to being used to detect cancer early, detection methods may also be used to determine whether treatment methods have been successful in eradicating cancer from a patient.
At present, methods for detecting most forms of cancer have relied primarily on the use of X-rays, nuclear magnetic resonance, nuclear radiation or invasive methods based on chemical laboratory analysis and biopsy. More recently, optical spectroscopy has been investigated as a means of detecting cancer.
For example, in U.S. Pat. No. 4,930,516, inventors Alfano et al., which issued Jun. 5, 1990, and which is incorporated herein by reference, there is disclosed a method and apparatus for detecting the presence of cancerous tissue using visible luminescence. According to the aforementioned patent, the tissue to be examined is excited with a beam of monochromatic light that causes the tissue to fluoresce over a spectrum of wavelengths. The monochromatic light disclosed in the patent has a wavelength in the range of 350-500 nm. The intensity at which the excited tissue fluoresces is measured either over a spectrum or at a predetermined number of preselected wavelengths, such as at 531 nm, 522 nm and 633 nm. The patent further teaches that one can then determine the carcinomatoid status of the tissue in question by comparing the detected spectrum, one or more peak wavelengths of the detected spectrum, or a ratio or difference of particular wavelengths from the detected spectrum to standards obtained from known tissues.
In U.S. Pat. No. 5,042,494, inventor Alfano, which issued Aug. 27, 1991, and which is incorporated herein by reference, there is disclosed a method and apparatus for detecting the presence of cancerous tissue using native visible luminescence. In accordance with said patent, the tissue to be examined is excited with a beam of monochromatic light having a changeable wavelength that causes the tissue to fluoresce. The intensity at which the excited tissue fluoresces at a preselected wavelength is then measured. The patent discloses that an excitation spectrum for human breast tissue was obtained by scanning from 300 nm to 500 nm at an emission wavelength of 520 nm. The patent further teaches that one can then determine the carcinomatoid status of the tissue in question by comparing the detected excitation spectrum, one or more peak wavelengths of the detected excitation spectrum, or a ratio or difference of particular wavelengths from the detected excitation spectrum to standards obtained from known tissues.
In U.S. Pat. No. 5,131,398, inventors Alfano et al., which issued Jul. 21, 1992, and which is incorporated herein by reference, there is disclosed a method and apparatus for distinguishing cancerous tumors and tissue from benign tumors and tissue or normal tissue using native fluorescence. According to one embodiment of said patent, the tissue to be examined is excited with a beam of monochromatic light at 300 nm. The intensity of the native fluorescence emitted from the tissue is measured at 340 nm and at 440 nm. The ratio of the two intensities is then calculated and used as a basis for determining if the tissue is cancerous as opposed to benign or normal. According to another embodiment of said patent, excitation profiles may be employed to distinguish cancerous tissue from benign or normal tissue. For example, the patent teaches that excitation spectra obtained by measuring the intensity of fluorescence at 340 nm as the excitation wavelength is varied from 220 nm to 325 nm are different for cancerous and benign breast tissues.
In U.S. Pat. No. 5,413,108, inventor Alfano, which issued May 9, 1995, and which is incorporated herein by reference, there is disclosed a method and apparatus for examining a two-dimensional region of a tissue sample. In accordance with said patent, this is accomplished by illuminating, i.e., exciting, the two-dimensional tissue sample with light at a first wavelength. The resultant fluorescence is then measured at an emission wavelength as a function of location within the two-dimensional tissue sample. The two-dimensional tissue sample is then illuminated again with light at a second wavelength, and the resultant fluorescence is measured at the same emission wavelength. The two excitation wavelengths and the emission wavelength are appropriately chosen so that the ratio or difference of fluorescence intensities at the emission wavelength is indicative of the carcinomatoid condition of the tissue. A value, such as a ratio or difference, of the respective intensity measurements obtained at each location of the tissue sample is then calculated. These values are then compared to appropriate standards, and the results are depicted in the form of a map. The invention is premised on the discovery that certain native, commonly-occurring molecules, such as collagen, NAD+/NADH, NADP+/NADPH, flavins, tryptophan and elastin, fluoresce differently in cancerous tissue than in non-cancerous tissue.